Electric control element



Oct.- 3l, 1.950 F. R. QUINN ELECTRIC CONTROL ELmmNT Filed Oct. 12I 1949Inventor-. Frederic p. Quinn,

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Patented Oct. 31, 1950 ELECTRIC CONTROL ELEMENT Frederic R. Quinn,Schenectady, N. Y., assignor to ,General Electric Company, a corporationof New York v Application October 12, 1949, Serial No. 121,005

6 Claims.

1 The present invention relates to a control element or deviceresponsive to changes in ambient thermal conditions, that is, to changesin ambient temperature or heat transfer conditions. It is specicallyconcerned with an improved fluid level control device of the thermalresponsive t e.

yi general object of the invention is to provide -a new and improvedthermally responsive control element of simple, compact and ruggedconstruction which is responsive to changes in ambient thermalconditions.

For additional objects and features of the invention, reference is madeto the following detailed description taken in conjunction with the`accompanying drawing in which Fig. 1 is an elevational view of thedevice of the present invention; Fig. 2 is a longitudinalcross-sectional view thereof; Fig. 3 is a sectional View along lines 3 3of Fig. 2; Fig. 4 is a view of certain components oi the device in thepartially assembled state; and Fig. 5 is a view of another part of thedevice prior to assembly.

The embodiment of the invention illustrated in the drawing comprises ametal casing or housing I including a metal tube or sleeve 2 and a capS, which housing encloses a temperatureresponsive resistance element 3and a heating coil 4. The resistance element and heating coil aresupported in heat interchange relationship by a metal tube 5 which ispreferably of copper or other metal having good heat transferproperties. The tube 5 which extends concentrically within the sleeve 2and spaced from the walls thereof. comprises an upper portion 6 aboutwhich the heater coil '4 is wound. The coil is insulated from the tube 6and held in place thereon by means of layers of insulation 'I and 8. Formaximum heat resistance the insulating layers preferably comprise glassber tape impregnated with an organo-polysiloxane resin.

The lower portion II of the copper tube is of somewhat larger diameterthan the upper portion and is adapted to contain the element 3. In theillustrated modification, the element 3 comprises a metal cup-shapedcase I2 forming one contact and containing a mass of temperatureresponsive resistance (thermistor) material I3 in which is embedded asecond contact in the form of a wire I4. resistance material I3 ispreferably a mixture of metal sulfides of the type described and claimedin my copending application Serial No. 106,293, filed July 22, 1949, andassigned to the same assignee as the present invention. A preferred Thetemperature responsive material consists `of a sintered mixture of 15 to35 percent by weight of calcium sulde, 0.03 to l0 percent molybdenumdisulde, balance silver sulfide. The open top end of the case I 2 issealed by a suitable insulating material I5 such as a heat-hardenablepolysiloxane resin. The interior diameter of the lower portion II of thetube and the exterior diameter of the case I2 are such that the elementsnugly ts within this part of tube 5 along most or all of its length.The portion I l of the tube is in turn enclosed within the ycylindricalportion I6 of cap 9, which portion extends a substantial distance withinsleeve 2 so that the resistance element is in good heat exchangerelationship with a metal cap!) as well as heating coil 4.A By thisarrangement heat supplied by the coil 4 to element 3 is dissipated bycap 8 and the adjacent portions of sleeve 2 at only a moderate rate whenthe cap end of the device is surrounded by air or other gas but at asubstantial rate when immersed in a iluid, which term is intended tocover both liquids and iinely ivided solids such as coal dust, sand,etc.

Three-wire cable 20 provides means for connecting the heater andthermistor element to a source of power and to the remaining componentsof a suitable control system. The end of the cable extending into theupper end of the housing I is secured to the tube 5 by a strain reliefmember 2|. This member, as is shown particularly in Fig. 4, includes anannular center section 22 engaged by a pair of peenedover ears 23 on theupper end of tube `5 and a pair of upwardly eX- tending arms Z4 and 25,both of which overlap the outer sheath of cable 20 and one of which hasa pair of ears 2'! wrapped around the cable in clamping relationship.

One end of ,heating coil 4 is connected to electric current supply 30 bya conductor 3| spotwelded to the coil and to wire 32 of cable 2!) whilethe other and lower end of the coil is spot-Welded to a ribbon conductor33 which passes through aperture 33a in tube 5.and upwardly through thetube with the upper end thereof connected as by spot-welding to arm 24of the metal strain relief member 2I. The other arm 25 of this member isin turn electrically connected to wire '34 which in turn is'connected tothe current supply 30 to complete the circuit for the heater.

Thefthermistor element is preferably but not necessarily operated on alow voltage circuit so that the power supply for the circuit includingthis' element suitably comprises the current from the low voltagewinding of transformer 35. 'I'he control device is inseries with coil36a of a relay 3E with the circuit comprising conductor 31 connectingthe relay with the transformer, wire 38 of cable 20 connected throughribbon conductor 40 to the center contact wire |4 of the thermistorelement 3, and ribbon conductor 4| connecting the case I2 of element 3to arm 24 of the stress relief member 2| which in turn is electricallyconnected through conductor 34 to the transformer 35.

Additional features of construction of the device will best beunderstood from a considera tion of the manner in which it is assembled.

Heater coil 4 is rst wound on the upper por-- tion of tube 5 and leads24 land 3| attached to the ends of the coil. The strain relief member isthen connected to the upper portion of the tube by peening-over ears.TheY thermistor element 3 with ribbon leads 4|] and 4| attached theretois then inserted into the bottom portion of tube 5 with a glassinsulating tube 46 surrounding the center lead 4|] and extendingupwardly through the top of the tube 5. Heater coilconnector 33 andthermistor lead 4| are spot-welded to arm 24 and lead 4E] connected towire 38. A glass ber tape sleeve wound between glass tube 48 and theinsulation on wire 38v completely insulates lead 43 from adjacent partsof the device. The strain relief member 2| is then secured to cable 2liby wrapping ears 2 about the cable and a second layer or sleeve 48 ofglass ber tape applied about the lower portion of the strain reliefmember to enclose part of this member and wires 34 and 33 leavingconductor 32 outside the sleeve to permit connection thereof to heaterlead 3|. A final insulating layer 49 of glass tape is then applied fromthe heater coil insulation 8 upwardly to enclose all of the strainrelief member 20.

This assembly is next inserted into sleeve 2 until the lower end of thetube 5 extends beyond the lower end of the sleeve. After applying alayer of varnish such as a polysiloxane resin varnish to the exteriorsurface of the portion of tube 5, cap 9 originally having theconstruction shown in Fig. 5 is slid over this portion and anchoredthereto by upsetting the rim of part i6 of the cap over the shoulder 5i!on tube 5. A coating of resin is then applied to the cuter surface ofthe cylindrical 'part i6 and the cap inserted into the sleeve. To sealthe sleeve and cap, the lower rim of the sleeve is spun into recess 5|of the cap and flange 52 of the cap spun back over the sleeve to providea pressure-tight joint, as shown in Fig. 2.

As thus assembled, the control device is adapted to be connected bymeans of its flared upper end 55 (Fig. l) to a conical nipple 55 bymeans of nut 51. The nipple in turn can then be connected to afluid-tight pipe or conduit 58 of a length suitable to permit suspensionof the device into the container holding the liquid whose level is to becontrolled.

For most control applications the thermally responsive elementpreferably comprises a material I3 having a low or zero resistance at anelevated temperature and a high resistance at the Vten'lperature of theliquid, the level of which is being controlled. In operating such adevice, a constant quantity of heat is supplied to the element 3 byheater coil 4. When the control device is suspended in air as, forexample, into a container above the surface of a body of liquid whosemaximum depth is to be controlled, the heat from the coil is sufficientto reduce the resistance of material |3 to a minimum so that relay 36 inseries with the element is energized to close or maintain closedcontacts 53 of a circuit (not shown) energizing, for example, a motordriving a pump for supplying liquid to the container. When the lower capend of the device is immersed in the liquid, heat is conducted away fromthe element and its temperature lowered to a point where its resistanceapproaches a maximum value sufficient to deenergize the relay, therebyopening the motor circuit and stopping the pump. By employing athermistor material of the above-mentioned sulde type and a stainlesssteel cap for the housing with the cap in direct heat exchanging contactwith a substantial portion of the thermistor element, the element reactsver'y quickly and positively to a change in ambient temperature or heattransfer conditions.

While a specic embodiment has been shown for purposes of illustration,it is obvious that the invention is not limited thereto and the appendedclaims are intended to cover all such modifications as fall within thetrue spirit and scope of the invention.

What I claiml as new and desire to secure by Letters Patent of theUnited States is:

1. A control device responsive` to changes in ambient thermal conditionscomprising a housing having a closed end portion composed of a heatconducting material, a heat conducting support within said housing andhaving a tubular end portion in Contact with the closed end portion ofsaid housing, a temperature responsive resistance element in saidtubular end portion of said support in heat exchange relationship withthe closed end portion of said housing and heating means surrounding theupper en d of said support.

2. A control device responsive to changes in ambient thermal conditionscomprising a tubular housing having a closed end composed of a heatconducting material, a heat conducting tubular member concentricallyarranged within said housing and having one end in contact with theclosed end of said housing, a temperature rr sponsive resistance elementsaid one end of said tubular member and in heat exchange relationshipwith the closed end of said housing, and heating means surrounding theother end of said tubular member.

3. A control device comprising a tubular housing member, a vcap of heatconductive material closing one end of said housing member and having acylindrical portion extending into said housing, a hea-t conductingsupport member within said housing, a temperature responsive resistancelelement supported within one end of said support member in heatexchange relationship with said cap, and heating means adjacent theother end of said support member and arranged to heat said resistanceelement continuously and at a fixed rate.

4. A liquid level control device comprising a housing including atubular member, a cupshaped metal cap closing one end of said memberwith the walls thereof extending into said member, a metal tube withinsaid housing and having a lower end portion surrounded by and in Contactwith said walls of said cap, a temperature responsive resistance elementwithin said end portion of said tube `and heating means adjacenttheupper end of said tube.

5. A liquid level control devicefor controlling the level of a. liquidcomprising a housing including'a metal sleeve, a metal cap closing oneend of said sleeve and comprising wall portions extending into saidsleeve, a, metal tube concentrically arranged within said sleeve withthe lower end thereof surrounded by and in contact with the wallportions of said cap, a temperature responsive resistance elementlocated within and in Contact with the lower end of said tube, heatingmeans surrounding the upper end of said tube for maintaining theresistance element at an elevated temperature, contact of said cap witha liquid serving to cool said element below said temperature.

6. A liquid level -control device for controlling the level of a liquidcomprising a housing including a metal sleeve, a metal cap closing oneend of said sleeve and comprising wall portions extending into saidsleeve, a metal tube concentrically arranged within said sleeve with thelower end thereof surrounded by and in Contact with the Wall portions ofsaid cap, a temperature responsive resistance element consisting of asintered mixture of l5 to 35 percent calcium sulfide, 0.03 to 10 percentmolybdenum disulfide,V

balance silver sulde, said element being located within and in contactwith the lower end of said tube, heating means surrounding the upper endof said tube for maintaining the resistance element at an elevatedtemperature, contact of said cap with a liquid serving to cool saidelement below said temperature. v

FREDERIC R. QUINN.

REFERENCES CITED UNITED STATES PATENTS Name Date Simmons Oct. 12, 1915Number

